: 1993 Exploding Intake Plenum

09-20-05, 07:19 PM
Several days ago when starting my Allante for the first time in the morning the intake plenum actually exploded, it blew off the end near the power steering pump. I have since gotten a used one with injectors and all in tact. After reassembly it won't start- sounds as though it wants to start. The battery went dead after several days with the hood open. It was deduced that the fuel pressure sensor allowed the plenum to fill with excess gas and exploded after a mere nano second of cranking in the morning. Any ideas on what next - fuses were okay for the injectors. I just got these codes off it - P31 P52 P95 P109 No BCM Codes PCM?

09-20-05, 07:28 PM
P031 (E031) .................................................. ... Shorted MAP Sensor
P052 (E052) .................................................. ..... PCM Memory Reset
P095 (E095) .................................................. Engine Stall Detected
P109 (E109) ....... Keep Alive Memory (KAM) Reset/PCM has lost primary battery power

THe only code that concerns me is P031 as to whether or not that would cause your problem, I will leave that to someone else.

I am not sure I agree with the conclusion that the fuel pressure regulator caused this, I believe you may have a leaky injector. I would be VERY careful with this problem, if this continues and fuel gets into a cylinder you COULD hydrolock the engine and put a rod through the side if it.

09-20-05, 07:52 PM
I got the injectors that came with the used plenum- I have not disassembled or even touched all that under the cover.

09-20-05, 08:43 PM
I would replace the map sensor. The pressure created by the explosion probably cracked it in two.

09-20-05, 08:46 PM
by the way - one of the main reasons why cadillac didn't recall the plastic 93-94 fuel rails was because it was "inside the intake manifold" and deemed "safe" in the event of a fuel leak. Yeah, sure sounds like it. http://cadillacforums.com/forums/images/smilies/icon_rolleyes.gif

Good thing nobody was standing under your hood when you started it up. Got any pictures? I would SERIOUSLY consider bringing in a lawyer to get cadillac to pay for your damages. Maybe a recall of these fuel rails would finally make all northstars safe.

09-20-05, 08:56 PM
I have many photos- tried posting them- I will send some if you like. Where may I ask is the map sensor. I really need this running to get to work tomorrow.

09-20-05, 09:17 PM
I missed a code P053 - Distributor Signal Interrupt. If that has something to do with timing I would believe it- it really sounds as though it wants to start......

09-20-05, 09:48 PM
This IS a northstar, correct?

P053 is a 4x reference signal interrupt from the ICM.

It could be just that wire that's faulty, or it could be due to trying to start it and then having the battery die, or ....

Looking at the coilpack, with the spark plug terminals being "up", remove the top connector on the right side (looking towards the firewall). Make sure there is no corrosion anywhere in it's 6 pins. I'd have to check the manual for any further instructions beyond that.

The MAP is under the intake top cover, near the throttle body, and may be either bolted down, or just held in with a grommet. I don't know in a 93. If it did explode, it may be just lying around in pieces... But you mentioned getting a new manifold, right? You should've got a new sensor as well. In that case, it may be just due to the old manifold's explosion.

09-20-05, 10:01 PM
Here we go - "P031 could be set during an engine backfire, which would cause a rapid increase in MAP value"

on code 53 - it says "check engine compartment fuse block fuse A13"

Do you know where the ICM battery connector is? It wouldn't hurt to check for proper voltage there.

09-20-05, 10:26 PM
Yes - it is a Northstar. With an absolute piece of junk voltmeter I tried getting a reading off the coil packs while my daughter was cranking the engine- got nothing but when checking the remote battery post got 12v so I know I was grounded. So- I got no spark coming off any of the coil packs- thoughts anyone?

09-20-05, 10:30 PM
I have no under the hood A13 - it is an Allante if not mentioned. I will look at all the under hood maxi fuses and A13 in the center console-

09-20-05, 11:05 PM
Yes - it is a Northstar. With an absolute piece of junk voltmeter I tried getting a reading off the coil packs while my daughter was cranking the engine- got nothing but when checking the remote battery post got 12v so I know I was grounded. So- I got no spark coming off any of the coil packs- thoughts anyone?

uhh.. reading off the tip of these?


(brass in this picture)? If so you may have killed your volt meter.

Look for the connector that looks like this:

but has 3 pins, and is on the driver's side of the coilpack. With the key in run, but the engine OFF, measure the voltage between the two outer pins. You should have 12 volts. If not, you've got a fuse/wire problem.

09-20-05, 11:07 PM
I have no under the hood A13 - it is an Allante if not mentioned. I will look at all the under hood maxi fuses and A13 in the center console-

Sorry, you're right, I'm looking at a Seville/deville/eldo service manual. I can probably pull up the wiring diagram if you don't find 12 volts at the connector.

09-20-05, 11:27 PM
I have 12v at the connector as you described. The voltage meter still works- perhaps had wrong setting when attempting high voltage coil reading- what next?

09-21-05, 01:01 AM
I am not so sure it is not a fuel issue- I hear the pump running behind me- it shuts off and when I check the relief valve on fuel line there is no pressure or gas escaping. I think it would be impossible to get the two fuel lines that come up reversed- I also think those connectors are leaking a bit- how in the world do those get re-used successfully?

09-21-05, 01:54 AM
It would be easy to check fuel pressure with a gauge if you have one. It should be about 40-45psi when you turn the key on. The fuel lines are not swappable, as the return line is a different size. If your connectors are leaking, they may not be fully seated, or they may require replacement.

Any small steady leak will drain your fuel pressure fast. You could also have another faulty fuel pressure regulator, either leaking into the manifold, or not allowing fuel to pressurize. A leaking injector is also a possibility, especially when used parts of unknown background are used.

09-21-05, 02:32 PM
Any thoughts on replacement fuel line material- it seems impossible to re-use the existing bizzare compression fittings.

09-21-05, 02:58 PM
I would try replacing the o-rings first. Much simpler. You'd have to get them at the dealer. Are they threaded, or are they the "quick connect" snap on kind? Because I don't think you can replace the o-ring in the quick connect...

09-21-05, 03:45 PM
It is like a receptacle that you push one end into- then 4 small tabs prevent fitting from pulling apart. The metal fitting is fused to the end of the fuel line from tank. It connects to the line that comes out of the intake plenum. I can't see it being that reusable without leakage issues.....

09-21-05, 04:39 PM
Yes, that's the quick connect. They are meant to be reuseable, I've probably undone mine 10+ times in the past year. Never had a leak. Either it's not fully seated, or you scratched/gouged the o-ring seal. I don't know how you'd repair it, as the fuel line is nylon.... You may have to replace the entire fuel line.

09-21-05, 06:38 PM
I never got down into the receiving end- is it safe assume that a decent tire pressure gauge will work on the relief valve? After or while cranking I should either get a reading or the very least gas spraying out of the valve? I hear the fuel pump running. Is there a filter to get clogged?

09-21-05, 06:50 PM
While cranking and pushing in valve on fuel line a good solid stream with some velocity came out of the valve. Ten months ago I patched small pin hole leak that did not affect how the car drove - I do not think that there is a sufficient leak at the connector that would totally prevent the engine from starting. I do have 12 volt going to the coils but am not sure if it getting to the plugs. Should I pull the cover off of the plenum? I really need help - and I really need this running tonight. It will chug for 5 seconds on a blast of starter fluid. Could explosion of pushed me out of timing? Perhaps I am out of the computer perameters.

09-21-05, 07:48 PM
The intake plenum cover is off- there is not any smell of gas- can it be started this way or attempted? I am not really sure what to be looking for. Gas in the line but not in the rail of injectors??? SOS SOS SOS SOS

09-21-05, 08:08 PM
Sorry for the delay,

Do NOT start the engine without the cover. It's like starting the engine with the pedal to the floor - you'll hit redline and bounce off the revlimiter.

So it starts on starter fluid, correct? Then you have isolated it as a fuel problem. Now we just need to figure out why it's not getting fuel.

You could be seeing a faulty fuel pressure regulator, causing any built up fuel pressure to be released back to the fuel tank...

You could have a completely clogged fuel filter.

You could have no power getting to the injectors.

You could have a bad fuel pump....

Start with the simple things. Check the injector fuses. Perhaps replace the fuel filter (make sure you release the fuel pressure, and be careful of hot lights or sparks or anything... work outside)... It would be VERY helpful to have a fuel gauge at this point. A bike pump isn't really an option, the gas will probably eat it apart.

The explosion wouldn't have affected the computer or timing, unless the ignition module and/or coils were damaged. It's also possible that some wires were cut or torn, but that should be easy to see, plus you said it starts on the starting fluid, so it doesn't really sound like that's the problem.

09-21-05, 08:28 PM
1000 thanks-

The running for 5 seconds on starting fluid is a bit chuggish and will not start every time that way. I took an old piece of hose and put it over the nipple on the regulator- I then sucked- it could hold pressure that way. Should I put the cover back on? All the fuses and circuits are good to the injectors (starting on the fluid confirms this?) It sounds as though it really wants to start. The pump seems to run for a full 10 seconds even when only turing ignition to run off run off run off run off. Ideas???

09-21-05, 08:44 PM
If you want to fix this tonight, you need to get a fuel pressure gauge and get some readings.

Another thing it could be is a bad oil pressure switch. If it gets stuck open, your engine won't run because the switch controls the fuel pump. It tells the FP to turn on when it reads 4 psi. If it's broken, it won't turn on the fuel pump, and you'll only be able to run on the small amount of fuel from the "prime" when you first turned the key on.

Again, a fuel gauge would be able to detect this as well. If during cranking, the pressure instantly drops to 0 and doesn't recover, then you know that's what the problem is.

09-21-05, 08:57 PM
I am getting some chugging idling out of it. The fuel pump which I am certain is right behind me is almost constantly running. Will a regular tire gauge work on the fuel rail? Also when my daughter was cranking engine I was getting good flow and velocity steaming out the pressure valve.....I am not getting anything out of the relief valve unless the engine is cranking.

09-21-05, 09:04 PM
No, it won't. Not unless you like fuel sprays and fires. If it's running, perhaps you can get some more codes. At this point, anything would help. I have no idea what you're talking about in re: pressure valve and relief valve. There should only be a schrader valve (looks like a bike tire valve).

09-21-05, 09:06 PM
cover is back on- it will chug on its own for 10 seconds now- when the fuel pump is running you can hear gas gurgling through the plenum cover- there is also a clicking sound under the cover too- its hard to determine where it is at.

09-21-05, 09:07 PM
Hmm... could be that you just have some air trapped in the fuel rail... That should work itself out... The clicking is probably the injectors.

09-21-05, 09:16 PM
sorry- i was refering to the schrader valve- there was little trickle when I depressed the center pin on the valve after it chugged for 10 seconds- when cranking the engine with valve pin depressed there was solid flow (I know its not factual pressure reading)

09-21-05, 09:25 PM
31 52 53 74 95 109

09-21-05, 09:46 PM
It seems as though it is duping fuel back into tank- there is quite a bit of running liquid sound under the cover- it would seem impossible for air not to be out at this point. Being the dead battery - used intake plenum with fuel rail/injectors is there not a learning program for reprogramming idle? Can I force this?

09-21-05, 10:22 PM
The computer runs a generic fueling program that is capable of running in a wide range of "problems". The fact that it's not running well means you have some major problem.

there usually is a bit of "running water" sound when it first pressurizes... I don't know what to tell you at this point. You're welcome to try swapping the fuel pressure regulators out. At this point, all i can do is speculate without being given numbers...

09-21-05, 10:24 PM
You've been an incredible help!

09-22-05, 10:45 AM
It is being towed to the local Cadillac dealer - I shall prepare for the shafting...........

09-22-05, 11:47 AM
It would've been cheaper to diagnose yourself, but considering the time frame you needed it up by, and the lack of tools, it was probably a good idea.